That's kind of an open-ended question for an "opinion poll" but here goes:
I'd always been into world building and SF, long before I discovered RPGs. As a kid my wall was covered with star maps that I'd invented and pictures of rockets and so on. Looking back on it now that seems a bit weird.
Then my family moved to a new town (on a new continent) just in time to start high school grade 10. I didn't know anybody. But the school had a "club daze" thing at the start of the semester and there was this one group trying to drum up membership for the school D&D club. I had no idea what it was about so I signed up for it anyway, along with a few other school clubs. After about 6 months, and by now being completely hooked, I tried my hand at GMing. Initially still D&D (specifically AD&D) ... but I always liked SF so my first campaign mutated fairly quickly into a bizzaro SF thing, complete with massed Dalek hordes (which no one in my group had even heard of at that time). Then one day, whilst browsing at my FLGS, out of curiosity I picked up JTAS 6 and 8 (#7 was sold out). A month later I returned and bought the basic Traveller game box and started collecting all things Traveller.
In the group I was now in (which had evolved out of the school D&D club after a blanket ban on all RPGs in the school) we took turns GMing, but everyone had their own game: I was the Traveller GM, one friend was the AD&D GM, another was the Star Trek (FASA) GM, and so on. Of course over the years since then we all tried several others (C&S, Rolemaster, Space Opera, Twilight 2000, Paranoia, Droids, Call of Ctulhu. Gamma World, Boot Hill, etc) but I always came back to Traveller.
But the point is that I'd already learned the basics of how to roleplay, and had had a bash at GMing and world building, so Traveller just came naturally.
And back then it was also handy because, after character generation, I could largely "freeform it" without needing to memorize many tables. With the school ban on RPGs this was important as being found in the school corridor at lunch time with an RPG book earned you a trip to the Principle's office. I felt a bit sorry for the AD&D GM as he had dozens of tables to memorize (this was pre-THAC0 and so there was a separate 20x20 ToHit table for each character class). To this day I tend to GM semi-freeform rules-lite just-wing-it. In retrospect that school ban kind of did me a favour, I think I'm a better GM now than I might have been otherwise.
Since those early days I've experimented with different things ... props, sound FX, non-linear story lines ... to try and keep the games fresh and improve the in-character roleplaying aspect of our gaming. And by being in groups that take turns to GM, and GM different games, I've continued to pick up new tricks from my fellow gamers.
Anyway, there you go.